1. Field of the Invention
This invention relates to an optical system for a color television camera device which has a first light-separating filter disposed in a substantially afocal light beam between the front group and the rear group of the relay portion.
2. Description of Prior Arts
According to the prior arts known to the applicant, the conventional color television camera device has a color-resolving filter disposed behind an objective lens.
For example, British Patent specification No. 1,207,282 published Sept. 30, 1970 discloses a color television camera device, in which the image of an object to be photographed is formed on a field lens through an objective lens, a front group of a relay lens is disposed in the light beam from this field lens, a tricolor-resolving optical system is further disposed in the light beam from the front group of the relay lens, and the rear group of the relay lens disposed in the light beams from the color-resolving optical system, whereby color-resolved images are obtained.
Such device, however, has been disadvantageous in that it tends to elongate distance between the objective lens and the pickup tubes, because the object image is once formed on the field lens.
U.S. Pat. No. 2,971,051 issued Feb. 7, 1961 and U.S. Pat. No. 3,202,039 issued Aug. 24, 1965 disclose color television cameras which use an objective zoom lens of long back-focus and a color-resolving optical system disposed in the back-focus portion of the zoom lens. In these devices, pickup tubes must be arranged radially with the consequent increase in height of the camera device.
On the other hand, the device shown in U.S. Pat. No. 2,971,051 has been successful in reducing its height by using a reflection mirror to arrange the pickup tubes in parallel each other, although such arrangement inevitably necessitates the back-focus of the zoom lens to be further lengthened, thus making it very difficult to design the lens.
Also, U.S. Pat. No. 3,547,521 issued Dec. 15, 1970 discloses an arrangement, wherein a color-resolving filter is interposed between the zooming section and the relaying section of a zoom lens. By adoption of such arrangement, the entire optical system becomes compact.